Musnad Ahmad Hadith 27593

It is narrated from Asma (may Allah be pleased with her) that the Prophet (ﷺ) said: “Whoever keeps horses as equipment in the way of Allah and spends on them with the intention of reward, then their being full or hungry, quenched or thirsty, and even their dung and urine will become a cause of success for him in his record of deeds on the Day of Judgment. And whoever keeps those horses for show, pride, and arrogance, then their being full or hungry, quenched or thirsty, and their dung and urine will become a cause of loss for him in his record of deeds on the Day of Judgment.”